1. Place pecans in a single layer on a baking sheet.
2. Bake at 350° for 8 to 10 minutes or until toasted.
3. Prepare mix according to package directions; pour batter into a greased 15- x 10- x 1-inch jelly-roll pan.
4. Bake at 350° for 25 minutes. Remove from oven, and top with marshmallows; bake 8 to 10 more minutes. Drizzle warm cake with Chocolate Frosting, and sprinkle evenly with toasted pecans.
Note: For testing purposes only, we used Duncan Hines Chocolate Lover's Double Fudge Brownie Mix.